Calutron ion source



Feb 17, 1959 E. J. LOFGREN 2,874,295

cALUTRoN 10N SOURCE Filed'May 8, 1946 JUPPL y Acca [en rl/v vu m65Jup/uy United States Patent O V CALUTRON ION SDURCE Edward J. Lo-fgren,Berkeley, Calif., assignor to the United States of America asrepresented by the United States Atomic Energy Commission ApplicationMay s, 1946, serial No. 668,112 s claims. (c1. 25o-41.9)

2,874,296 l Patented Feb. 17, 1959 ICC portion of a calutron, theshowing being in isometric perspective with portions of the structurebeing omitted for clarity.

Fig. 2 is a section on a horizontal plane of an ion source mechanism fora calutron in diagrammatic form.

Since the general construction of a calutron and the detailedarrangement of the portions constituting the environment of the presentinventive embodiment are well disclosed in the identified patent toLawrence and play no immediate part in the present invention, referenceis herein had only to a diagrammatic showing for simplicity inunderstanding and clarity of disclosure. It is understood that theentire mechanism operates in a. magnetic field, is supplied withelectricity in various appropriate circuits, and is, except for thepartsV referred to specifically herein, like the structure shown in thethe drawings and the accompanying description especially i .i

characterize a structure to which the present disclosure is mostapplicable.

In devices of this nature the practice is to passa stream of vapor orgas to be ionized 'to or into the vicinity of an electric arc. The arcis customarily of columnar form struck between a iilamentary cathode andan anode spaced apart in the direction of a magnetic field in which theentire structure functions. Ions are produced by collisions of the gasor vapor molecules with particles occurring in lthe arc and` are removed-from the arc or its vicinity under the urgency of `an electricaccelerating lield. This field is established between the arc mechanismand one or more, usually-two, accelerating electrodes spaced from thearc mechanism in the general direction of propagation of an ion beamconstituted by the withdrawn ions.

The operation of an ion source of the described kind is accompanied bythe production of large quantities of heat. The resulting hightemperatures have deleterious effects upon the materials of the arcmechanism and shorten the life of the arc structure to a uneconomicextent. Also the various particles generated by the operation of the arcbombard or sputter upon the adjacent mechanical surfaces and causedeterioration and erosion of an undesirable sort and quantity. Inaddition the ion stream owing from the arc block tends to erode and varythe shape of the surfaces of the aperture or orifice through which theions emerge. Since these surfaces are effective to establish the contourof the electric field existing in the vicinity and since the contour ofsuch field is instrumental in controlling the particular shape and focusof the ion beams, imperfect and improper action of the mechanism occursafter only a short initial operation.

It is therefore an object of the invention to provide means forwithstanding the ravages of the quantities of heat, erosion anddeterioration concomitant with the operation of an ion source of thecalutron type. 1

An additional object of the invention is to provide means for insuring aprotracted operation of the ionizing mechanism without substantialinterference with the trajectory or pattern of the lion beam.

An additional object of the invention is in general to improve arcionizing mechanisms.

A still further object of the invention is to improve calutrons ingeneral.

AOther objects of the invention together with the foregoing are attainedby the embodiments of the invention disclosed in the accompanyingdescription and drawings in the latter of which:

Figure 1 is a diagrammatic showing of the ion source 1 point.

Lawrence patent.

There is provided an ion source mechanism incorporating a source block 6preferably fabricated of metal having a good thermal conductivity suchas copper and mechanically supported upon a mounting stem 7 also servingas an electrical conductor. The source block 6 is formed with a normallycovered charge cavity 8 within which material to be ionized is placed.Customarily, the material is in a separate container or charge bottlecontaining granular material that evolves gas or vapor when heated.

To produce the desired effect the charge block 6 is provided With aplurality of heaters 9 effective to increase the charge temperature tothe gasifying or vaporizing Gas so evolved flows from the charge chamber8` through a passage 11 into a normally covered gas distribution and arcchamber `12 likewise constituted by a cavity in the arc block 6. Tostrike an appropriate arc there is arranged above the arc block 6 afilamentary cathode 13 disposed in the end of a cathode stem 14 carryingappropriate electrical leads and maintained, by means of a filamentsupply 2 and an arc supply 3, at the proper potential with respect tothe arc block 6 that the block also serves as an arc anode. The positionof the arc in the block is shown approximately by the stippled area 16in Fig. l.

Ions formed adjacent the arc are withdrawn from the arc block 6 throughan opening 17 leading from the arc chamber 12 to the exterior of theblock and being formed and defined by the facing edges of the forwardcoplanar walls 18 and 19 of the arc block. The margins of the opening 17are further defined by a pair of coplanar plates 21 and 22 defining asomewhat narrower slot 23 and preferably fabricated of a metal having ahigher resistance to temperature eects than the copper of the block 6and thus being preferably made of molybdenum. The plates 21 and 22 areheld in intimate contact with the walls 18 and 19 in order to facilitatethermal transfer from the plates to the block. Additionally, the furthermargins of the opening are dened by a supplementary pair of plates 24and 26, respectively, having their facing edges 27 and 28 beveled todefine a dihedral angle. The plates 24 and 26 are preferably formed of ametal such as copper having a high heat absorptive and transmittingproperty and are maintained in intimate thermal contact with the plates21 and 22.

By the provision of this arrangement the narrowest portion 23 of the arcslit is defined by resistant plates 21 and 22. These plates aremaintained at a feasiblev Some of the attributes of the arrangement ofFig. l are lattained in the modified embodiment disclosed -in Fig. 2wherein for the most part the structure is identical except that the arcshown by the stippled portion 31 is related lto -a pair of arc slitdening 4plates 32 and V373 dn such a fashion -that .many of the -ionswithdrawn Aby accelerating electrodes 34 and 36, suitably supplied byaccelerating voltage supply '35, do not directly impinge upon the plates`32'and 33.

. This is electuated by providing the plates with bevelled faces 37 and38 respectively defining a dihedral angle that converges in thedirection of eux of theions. Thus the contour of the arc plasma,represented by `the :heavy line 39,-is in part behind 4the are slitplates 32 and 33 and the portions 41 and 42 of ,the plasma thatprincipally tend `Ato .release lions away from the central `portion .44of .the ion Pstream are well masked -from the 'electric -iieldest-ablishedby the -arc `slit plates 32 and 33 andthe `acceleratingelectrodes 34 and 36. In lthis vfashion most of the ions ileaving thevicinity of the -arc `31 pass through the arc slit between the adjacentedges `of ythe plates '32 and 33 without limpinging thereon. As `aresult, the arc slits are vnot excessively eroded and are maintained insatisfactory operating condition for a substantial time.

In both modifications of the invention disclosed herein there :isafforded a mechanism effective to improve in general the operation ofVan ion producing rmechanism and calutrons in general.

What :is claimed is:

l. yIn .an ion rsource for a calutron, the combination comprising an arcchamber having an exit opening, mean-s forestablishing -an-electric arcin said chamber along the length of fsaid opening, a pair of molybdenumplates in thermal contact with the walls of said chamber and disposed onopposite sides of lsaid opening to form the margins thereof, and a pairof copper blocks in thermally conducting contact with said plates ltoform Lsubsequent divergingmargins of said opening.

2. In an ion source for 4a calutron, the combination comprising an arcchamber having an exit opening, means for establishing an electric arcin said chamber along the length of said opening, a pair of high meltingpoint plates in thermal contact with the walls of said chamber anddisposed on opposite sides of said opening to form the margins thereof,and a pair of highly heatconducting blocks in thermal contact with saidplates to form subsequent .diverging margins of said opening.

3. In an ion source for a calutron, the combination comprising an arechamber having an `enit opening, means for establishing an electricarc'in said chamber along the length of said opening, and multi-layerdevices mounted on the walls ofsadv chamber and forming-the margins ofsaid opening, an exposed one vof s aid layers being made up of a metalof high thermal conductivity and an inner one of said layers being madeup of a metal having a high resistance to ion bombardment.

4. I n an ion source for a.ca1utron, the combination comprising anarcchamber having anexit opening, -means for establishing an lelectric larcin said chamber along the length of said opening and laminated membersinrthermal contact with said igon source member and defining the Ifacingedges of-said opening, said vmembers .having different thermalconductivities and different resistances to heat.

5. In an ion source for a calutron, the combination comprising an arcchamber havingan exit opening, means for establishing :an electric -arcin said chamber alongfthe length .of said opening vand means includinglaminated plates defining the edges of s aid opening, vthe plates linthe narrowest part of saidopening having relatively lthe highestresistance to Ithermaldeterioration.

.References Cited in the file 0f this patent The Production andYFocusing of 'Intense 'Positive Ion Beams, by Tuve etal., PhysicalReview, volume 48, August l, 1935, pages 241-256.

